Using appropriate genetic crosses, C57BL/6J mice will be used to produce males, heterozygous females, and homozygous females affected with an X-linked dominant form of vitamin D resistant rickets (VDRR). We propose to study the development and appearance of craniofacial and dental abnormalities associated with this disease and to assess effects of therapeutic measures used in the treatment of VDRR in humans. We plan to use radiology, cephalometry, histology, histochemistry, and biochemistry to obtain our results.